The present invention relates to a newly developed driving system for data writing which prevents the problem of over write into non-selected display rows (shift rows) in a self shift type gas discharge panel, and particularly in a multi-row display panel.
The self shift type gas discharge panel of the present invention belongs to the field of gas discharge panels with an AC memory driving system wherein the information written in the form of discharge spots is shifted to the other end from the write end of the shift channel in such a manner that one period of the shift discharge cell arrangement is considered as one picture element and during the shift process a static display can be obtained by stopping the shift operation at particular discharge cell groups. Up to now, a variety of types have been conventionally proposed. Such a panel has an advantage that it can be reduced in size more than the ordinary display unit utilizing a CRT, in addition to excellent display functions based on the memory operation. Therefore, it is often employed as a monitor display and a keyboard display used for terminals of computer systems. The self shift display using such a panel is mainly intended for multi-row display, and the structure allows independent shift operation for display rows. For example, display data in non-selected display rows may be held at a specified location while new characters are written in or an update is carried out in selected display rows.
In such a multi-row display, the driving circuit is generally simplified and reduced in size by providing in common the write drivers for the write electrodes of the display rows.
However, when writing data into the selected display rows, such a structure allows the discharge spots to be generated also simultaneously at the write discharge cells of the non-selected display rows. Namely, such a structure has a disadvantage that an extra discharge, the so-called over-write, is generated at said shift discharge cells of the non-selected display rows in accordance with the condition of a wall charge at the surface of a dielectric layer corresponding to the shift discharge cells which are in-phase with said write discharge cells and adjacent to them. This over-write phenomenon will be explained in more detail by making reference to the multi-row display self shift type gas discharge panel providing the meander electrode structure proposed in U.S. Pat. No. 4,190,788 by Yoshikawa et al., assigned to the same assignee as the present invention. FIG. 1 schematically shows the electrode arrangement of such a panel. In this case, two shift channels SC1 and SC2 are represented in order to simplify the explanation, and a single display row is configured by a single shift channel. Each of these shift channels is formed between two respective Y electrode groups y1i, y2i (i is a positive integer) which are alternately arranged on the not illustrated lower substrate and have the meander pattern and two respective X electrode groups x1j, x2j (j is a positive integer) which are alternately arranged on the side of the upper substrate opposing said Y electrode groups. The surfaces of said electrodes are coated with a dielectric layer on the respective substrates, and the write electrodes W1, W2 are provided for the channels adjacent to the extreme right electrode x11 belonging to one X electrode group and opposing the extreme right electrode y11 of one Y electrode group. Thus the four groups of discharge cells ai, bi, ci and di are formed with 4-phases (phase A to phase D), between opposing portions of the electrodes, which are connected in common alternately and regularly and periodically arranged within the discharge gas space, and thereby the discharge spots generated by the write discharge cells w can be shifted sequentially along the arrangement of these discharge cells. Here, each write discharge cell w is formed on each shift channel between opposing portions of the write electrodes W1, W2 and the shift electrode y11 of each shift channel as a normal write discharge cell, and the write discharge area w' of the surface discharge mode is formed between the adjacent portion of each write electrode W.sub.1, W.sub.2 and the respective shift electrode x11 of each shift channel on the same substrate.
In the multi-row display structure, said two Y electrode groups are individually led out to two buses for each row (shown as Yj1, Yj2 for the jth shift channel or row, with j=1, 2, 3, etc) in order to make possible the shift operation of discharge spots for each display row, and these buses are connected individually to the Y shift drivers (not illustrated). Moreover, said two X electrode groups are respectively led out to the buses indicated as X1 and X2, with all display rows being connected in common as to these two electrode groups. Further, as explained above, said write electrode groups are led out with corresponding electrodes in each display row being connected in common and then connected to the corresponding write drivers (not illustrated).
In such a multi-row display self shift type gas discharge panel, while the shift operation is being carried out in order to write information into the selected write rows, the information already written into the non-selected display rows is kept in the display condition by the sway shift system (operation) in view of improving display quality.
FIGS. 2(A)-(D) show the driving voltage waveforms for attaining the shift operation and sway shift operation in the plurality of display rows. In this figure, in regard to the 1st, 2nd display rows (shift channels) SC1, SC2, the first display row SC1 is selected and the second display row SC2 is in the non-selected condition. FIGS. 2(A) and (C) show the electrode voltage waveforms applied to electrodes of the selected 1st display row and non-selected 2nd display row through the indicated buses, while FIGS. 2(B) and (D) show the cell voltage waveforms which are applied as the combined waveforms of said voltages applied to the electrodes of the discharge cell groups between the indicated electrodes of the 1st and 2nd display rows. As is apparent from these figures, the shift operation of the gas discharge panel having the meander electrode structure is carried out in such a way that four basic pulse trains indicated as 1 to 4 in the four steps t.sub.0 to t.sub.3 are distributed in the sequentially rotating illustrated manner to the plural buses. It is supposed, for example, that each display row is set in the static display mode (fixed mode) during the period from T.sub.0 to T.sub.1 as shown, in which the common shift voltage pulse SP is applied to the buses Y11 and Y21 for the two groups of Y electrodes of each row, and the shift voltage pulses SP with equal phase are applied to the two buses X1 and X2 for the X electrodes. On the other hand, the shift voltage pulses SP which have a phase difference of .tau..sub.e, corresponding to the time width of an erase voltage pulse after the rising and falling edges of the shift voltage pulses SP of the buses of the X electrodes, are applied to the buses Y12 and Y22 for the other Y electrodes of the display rows. As a result, the illustrated AC shift voltage pulse trains are applied to the adjacent discharge cell groups di and ai of the phases D and A of the display rows, while the narrow erase voltage pulses EP as indicated in FIG. 2(B) are applied by means of said phase difference .tau..sub.e to the remaining adjacent discharge cell groups bi and ci of the phases B and C. Therefore, the information of each display row written before the period from T.sub.0 to T.sub.1 is held at the adjacent two discharge cells di and ai in such a manner as to occupy in common a pair of adjacent discharge spots.
If data writing is required for the selected 1st display row SC1 in this static display mode, the following operation is performed. The write operation is carried out in the step in wherein the discharge cells di and ai of phases D and A are activated during one cycle of the shift operation consisting of the four steps t.sub.0 to t.sub.3. Namely, with reference to the step t.sub.0 in FIGS. 2(A) and (C), the write voltage pulses WP based on the common write information are applied to the write electrodes W1 and W2. Thereby, the write voltage waveforms indicated by w, w' are applied to the write discharge cell w and surface discharge write area w' of each display row. In other words, said write voltage pulse WP is applied directly as WP' to each write cell w, which provides as a result of cancellation the narrow pulse WP" across the surface discharge write area w', and the first discharge spots are respectively generated at the desired write discharge areas. At this time, since the shift pulses SP as indicated are applied to the cells ai of the phase A group to which the first shift discharge cells a1 of both display rows SC1 and SC2 belong, the discharge spots are simultaneously generated at said shift discharge cells a1 adjacent to the write discharge cells w by means of the priming effect of said write discharge spot. The discharge spots generated at the discharge cell a1 spreads to the two adjacent discharge cells a1 and b1 of the phases A and B in accordance with the change-over of said basic pulse trains applied in the next step t.sub.1. These discharge spots are, in the case of the selected 1st display row SC1, sequentially shifted to the other end (extreme left side) along the display row SC1 in such a manner that adjacent pairs of discharge cells b1 and c1, c1 and d1 are simultaneously discharged while the basic pulse trains as indicated are applied in the next steps t.sub.2, t.sub.3. During this period, the erase voltage pulse EP is effectively applied to the discharge cell groups from which the discharge spots are already shifted, and thereby the erase operation is carried out for the relevant discharge spots. The discharge spots of the discharge cells d2 and a3 which are written prior to this write operation are shifted sequentially as a3.multidot.b3.fwdarw.b3.multidot.c3.fwdarw. c3.multidot.d3--FIG. 3(A) schematically shows the write and shift operations of discharge spots in the selected rows in correspondence to the cell voltage waveforms of FIG. 2(B).
However, in the case of the non-selected 2nd display row SC2, since the basic pulse trains 1 and 3 which are applied to the buses Y21 and Y22 of the Y side during the time t.sub.2 are selected in the reverse relation to the basic pulse trains applied to the buses y11, Y12 of the Y side of said selected row SC1, the discharge spots located at said shift discharge cells a1 and b1 return to the cell a1 because the discharge cell groups of phases D and A are activated. In the next step t.sub.3, the shift discharge cells of the phases D and C are activated as in the case of the selected rows, but the discharge spots are shifted backward in succession toward the reversely adjacent cells of phases D and C from the cells of phases D and A. Due to such a sway shift operation, the discharge spots in the non-selected rows, corresponding to the write information generated as in the case of the selected rows by the write operation, are erased in this timing because the erase voltage pulse EP is applied to the relevant shift cell a1. Prior to this write operation, the discharge spots of the written discharge cells d2 and a3 are held in such a manner that these spots are swayed to the right or left to occupy the adjacent pairs of cells in the sequence of a3.multidot.b3.fwdarw.a3.multidot.b2.fwdarw.d2.multidot.c2 by the basic pulse application in accordance with said sway shift operation mode. FIG. 3(B) schematically indicates the sway shift operation in the non-selected rows.
As explained above, the self shift type gas discharge panel for a multi-row display of this type employs the structure that even if the write discharge spots are generated in the non-selected display rows simultaneously with the selected display rows, they are erased automatically, and therefore result in no problem for the display functions. However, when considering the case where excessive charges are accumulated at the surface of the dielectric layer covering an electrode which is in the same phase as the write discharge cell w', for example, in the non-selected rows, corresponding to the shifting to the adjacent shift discharge cell d1 of the phase D (but located one shift period away from the write cell), the firing voltage of said shift cell d1 is lowered more than the ordinary value due to such excessive charges. This phenomenon will be explained in more detail. The gas discharge panel of this type has a particular problem in that the charges are excessively accumulated at both ends of the shift channels when the shift operation of the discharge spots is repeated, and thereby an abnormal discharge easily occurs due to unequal distribution of the accumulated wall charges. From such circumstances, when the discharge spot is generated at the write discharge cell w (and surface discharge write area w'), unwanted erroneous discharge, namely the over-write occurs also at the adjacent shift discharge cell d.sub.1 by means of the priming effect and the shift voltage pulse at this time. Since this abnormal discharge spot which is not based on the information is not erased automatically, unlike the written discharge spot in each non-selected row, an erroneous display occurs, degrading the display quality of the panel.
This sway shift operation is explained in detail in U.S. Pat. No. 4,190,789 by Kashiwara et al. assigned to the same assignee as the present invention.